This proposal describes studies of dissipative transport processes in lipid bilayer membranes; and, experiments with isolated proximal straight, proximal convoluted, and cortical collecting tubules from rabbit kidney. One set of experiments with lipid bilayer membranes will analyze water and solute permeation in amphotericin B - cholesterol pores, and will also evaluate the stoichiometry of amphotericin B - cholesterol interactions involved in pore formation. The major goals of these experiments include: a detailed understanding of dissipative transport processes in channels having molecular dimensions; and, attempts to reconstruct in further detail models proposed by this laboratory for the structure of amphotericin B- cholesterol pores. A second set of experiments will involve attempts to reconstitute Na ion-dependent sucrase-isomaltase enzymatic activity from small intestine in lipid bilayer membranes. The experiments with renal tubules will involve: an examination of the role of HCO minus 3 in isotonic volume reabsorption; a study of "pump-leak" relationships for H ion transport and urinary acidification in proximal straight and cortical collecting tubules; an analysis of the transport of certain amino acids in proximal convoluted tubules; and, an evaluation of the mode of K ion reabsorption in proximal straight and proximal convoluted tubules. We anticipate, in that regard, that lessons learned from lipid bilayer experiments will serve as valuable adjuncts in the formulation of hypotheses designed to explain the molecular basis for transport processes in the renal tubule. BIBLIOGRAPHIC REFERENCES: Al-Zahid, G., Schafer, J.A., Troutman, S. L. and Andreoli, T.E. 1977. The effect of antidiuretic hormone on water and solute permeation, and the activation energies for these processes, in mammalian cortical collecting tubules: Evidence for parallel ADH-sensitive pathways for water and solute diffusion in luminal plasma membranes. J. Memb. Biol., in press. Schafer, J. A., Patlak, C. S. and Andreoli, T. E. 1977. A mechanism for isotonic fluid absorption linked to active and passive ion flows in the mammalian superficial pars recta. Am. J. Physiol: Renal, Fluid and Electrolyte Physiol., in press.